1. Field of the Invention
This invention relates to steel strapping and a method of manufacture, particularly to steel strapping which is intended for high temperature use, as in strapping hot steel coils, and which, after prolonged exposure at such high temperatures, exhibits superior strength retention.
2. Description of the Prior Art
It is usual to band hot rolled and coiled steel and hot tubular or bar steel products with steel strapping. Such strapping usually is produced from carbon/manganese steel, typically Containing on the order of 0.25 to 0.34 weight percent carbon and 1.20 to 1.55 weight percent manganese. The tensile strength of such conventional steels is substantially reduced on prolonged exposure to the prevailing high temperatures, e.g. about 1200.degree. F.
It is known that the combined addition of molybdenum and vanadium to carbon/manganese steels provides high strength at elevated temperatures (750.degree. F. to 1000.degree. F.), for example in U.S. Pat. No. 1,979,594. In that patent, steel of improved ductility and stress/shock resistance is achieved in a steel containing 0.10 to 0.30 weight percent carbon and 1.5 to 2.5 weight percent manganese, by the addition of 0.15 to 0.30 weight percent molybdenum and 0.05 to 0.30 weight percent vanadium, and processed either by annealing, normalizing or water quenching the steel, followed by drawing at 1100.degree. F.
Closely related technology exists with the alloying utilized in tool steels which also are alloyed with additions of vanadium, molybdenum and chromium. When heat-treated, tool steels exibit very high hardnesses and the ability to hold their hardness at elevated temperatures. The levels of alloying within this class of steels is much higher than with the present invention, with typical levels ranging from 0.5% to over 20%. Typically, the additions of vanadium and molybdenum exceed 1%, and are higher when temper resistance is required for the steel. For example, vanadium is a known addition to high carbon, e.g. 0.80-1.50% C, tool steels to improve hardness, for example as described in U.S. Pat. No. 1,952,575.
Oil well tubular products have been produced of carbon, manganese, silicon high strength, low alloy steels containing about 0.2 to 0.4% molybdenum, for example as described in U.S. Pat. No. 4,533,405.
As shown in U.S. Pat. No. 3,725,049, vanadium is known to enhance tensile strength, e.g. in steels containing 0.06-0.30% C, 0.30-1.5% Mn, up to 0.02% Si, and up to 0.02% acid soluble Al, and 0.02-0.40% V.